Effect of in-vitro pesticide exposure on oxidative burst potential of Sydney rock oyster hemocytes

Production of Sydney rock oysters (Saccostrea glomerata) has declined in Australia due to outbreaks of QX-disease (Marteilia sydneyi). The disease occurs in estuaries where the catchment has been modified by agriculture or urban activities. Scientific studies have shown that rock oysters are immuno-compromised prior to M. sydneyi infection and rainfall reduces the activity of oxidative enzymes involved in resistance to QX disease. Pesticides found in agriculture rainwater runoff have been suggested as a potential risk factor. The current study investigated sub-lethal concentrations of agricultural pesticides on the oxidative burst potential of S. glomerata hemocytes. Production of reactive oxygen species (ROS) by hemocytes in response to agricultural pesticides and a model immunogen (zymosan) was measured using an in-vitro chemiluminescence assay. Atrazine, diuron, chlorpyrifos and carbendazin at concentrations of 5 – 500 μg.mL⁻¹ had no effect on ROS production of S. glomerata hemocytes (p > 0.05). However, exposure of hemocytes to low levels of all pesticides (5 μg.mL⁻¹) and zymosan induced a significant increase in ROS production compared to zymosan controls (p <0.05). These results suggest that when rock oysters are exposed simultaneously to low concentrations of pesticides and pathogens, hemocytes overstimulate ROS production and oxidative damage to host cells could occur.